Η1 Coordination Mode Research Articles

Atomic-Level Structure of the Organic-Inorganic Interface of Colloidal ZnO Nanoplatelets from Dynamic Nuclear Polarization-Enhanced NMR.

Colloidal semiconductor nanoplatelets (NPLs) have emerged as a new class of nanomaterials that can exhibit substantially distinct optical properties compared to those of isotropic quantum dots, which makes them prime candidates for new-generation optoelectronic devices. Insights into the structure and anisotropic growth of NPLs can offer a blueprint for their controlled fabrication. Here, we present an atomic-level investigation of the organic-inorganic interface structure in ultrathin and stable benzamidine (bza)-supported ZnO NPLs prepared by the modified one-pot self-supporting organometallic approach. High-resolution transmission electron microscopy analysis showed a well-faceted hexagonal shape of ZnO NPLs with lateral surfaces terminated by nonpolar (101̅0) facets. The basal surfaces are flat and well-formed on one side and corrugated on the other side, which indicates that the layer-by-layer growth in the thickness of the NPLs likely occurs only in one direction via the expansion of 2D islands on the surface. The ligand coordination modes were elucidated using state-of-the-art dynamic nuclear polarization (DNP)-enhanced solid-state NMR spectroscopy supported by density functional theory chemical shift calculations. Specifically, it was found that (101̅0) nonpolar facets are stabilized by neutral L-type bza-H ligands with hydrogen bond-supported η1-coordination mode, while polar (0001) and (0001̅) facets are covered by μ2-coordinated X-type anionic bza ligands with different conformations of aromatic rings. Moreover, the ligand packing on (101̅0) lateral facets was determined using 13C natural abundance (∼1.1%) homonuclear dipolar correlation experiments. Overall, an in-depth understanding of the growth mechanism and the unique bimodal X-type/L-type ligand coordination shell of ZnO NPLs is provided, which will facilitate further design of anisotropic nano-objects.

Synthesis of highly sensitive and multi-response Eu-MOF, fluorescence sensing properties and anti-counterfeiting applications

A new Europium metal–organic framework (Eu-MOF), namely [Eu(dpa) (H2O)]·0.5(bpy)·4H2O}n (H4dpa = 5-(3,4-dicarboxyphenoxy) isophenic acid, bpy = protonated 4,4′-bipyridine) was synthesized and structurally characterized by elemental analyses, infrared spectroscopy, and X-ray single-crystal diffraction analyses. Eu-MOF shows a three-dimensional network structure based on EuIII ions and (dpa)4− ligands via µ4: η1, η2, η2, η2 coordination mode. Fluorescence analysis shows that Eu-MOF has excellent fluorescence sensing characteristics, which can efficiently and sensitively detect various pollutants in water: the limit of detection (LOD) of ratiometric fluorescence detection of ANI in water was 42.9 nM, which was better than the single-peak detection limit. In addition, the peak detection limits of Eu-MOF for Flu, ORN and NB were 120 nM, 27 nM and 94 nM, respectively. In addition, XPS, LUMO orbital energy level, fluorescence lifetime, ultraviolet absorption and other principles are used to explore the mechanism of fluorescence quenching. Surprisingly, Eu-MOF not only has excellent anti- counterfeiting ability and stability, can be used as anti-counterfeiting material in life, but also has good selectivity to Flu. Eu-MOF has obvious fluorescence quenching effect on Flu on paper under ultraviolet light, which can be used for rapid in situ imaging test paper of pesticide residues.

Oligomer and Polymer: Self Assembly of [Cp*Fe(η5‐P5)] and Ag(I) Salts of Bulky Weakly Coordinating Anions

AbstractReactions between the five‐fold symmetric building block [Cp*Fe(η5‐P5)] (A) and Ag(I) salts containing bulky weakly coordinating anions [TEF] and [FAL] ([TEF]=[Al{OC(CF3)3}4]–, [FAl]=[FAl{OC6F10(C6F5)}3]–) are presented. While, in the presence of Ag[TEF], A leads to the formation of a hitherto condensed 1D coordination polymer [{Ag(η2:η1‐A)2}]n[TEF]n (1), a new finite tetranuclear Ag(I) complex [{Ag4(η1‐A)2(η2:η1‐A)4(η1:η1‐A)2}][FAL]4 (3) was obtained with an Ag(I) salt bearing the weakly coordinating anion [FAl] increased in size. Various coordination modes (η2:η1; η1:η1 and η1) of A were observed in the solid‐state structure of 3, reflecting the adaptive coordination behavior of A towards Ag(I) ions. Structural modifications of the 1D polymer (1) can be controlled by the addition of a limited amount of MeCN yielding the unwound heteroleptic 1D polymer [{Ag(MeCN)2}3(η1:η1:η1‐A)2]n[TEF]3n (2). Moreover, in the presence of MeCN, the finite oligomeric compound 3 can also be converted into a new heteroleptic 1D polymer [{Ag(MeCN)}4(η1:η1‐A)5(η2:η1‐A)2]n[FAL]4n (4). The solid‐state structure of 4 discloses the existence of a unique 1,1,2‐η2:η1 (π,σ) coordination of A along with 1,3‐η1:η1 (σ) and 1,2‐η1:η1 (σ) coordination modes, while 1,2,4‐η1:η1:η1 (σ) coordination modes of A were found in 2. As revealed by X‐ray crystallography, in all the cases, the cationic moieties are well separated from the weakly coordinating anions in the solid state.

Synthesis, Structure and Chemical Bonding of Polyantimony Clusters Containing Coinage Metals [M2Sb14]4– (M = Cu, Ag)

Comprehensive SummaryBinary polyantimony clusters, namely [Cu2Sb14]4– and [Ag2Sb14]4–, containing coinage metals, were successfully synthesized and characterized, in which two homoatomic Sb73– subunits are bridged by two coinage metals in η4:η1 and η1:η1 coordination modes, respectively. In [Cu2Sb14]4–, two bridging Cu ions and two Sb atoms form a planar rhombic unit, which was revealed to have antiaromatic properties by theoretical calculations. Further electron structure and bonding analysis confirmed the presence of delocalized bonds in the rhombic unit and the metallophilic interaction between two formal M+ ions.

A New Cd(II)-Based Coordination Polymer for Efficient Photocatalytic Removal of Organic Dyes.

Coordination polymers (CPs) are a diverse class of multi-dimensional compounds that show promise as photocatalysts for degrading dyes in polluted water. Herein, a new 1D Cd(II)-based coordination polymer with the formula [Cd(bpyp)(nba)2] (1) (bpyp = 2,5-bis(pyrid-4-yl)pyridine and Hnba = 4-nitrobenzoic acid) is synthesized and characterized. In 1, the two carboxyl groups of two different nba- ligands show μ2-η1:η1 and μ1-η1:η1 coordination modes to connect the CdII centers and sit on either side of the chain along the b direction. The produced CP 1 was utilized as the photocatalyst in the process of the photodegradation of methyl blue (MB), methyl orange (MO), rhodamine B (RhB), and methyl violet (MV) dyes when exposed to UV light. The photocatalytic degradation activities of CP 1 were analyzed, and the results suggest that it exhibits an extraordinary efficiency in the degradation of MB, MV, MO, and RhB. RhB has a 95.52% efficiency of degradation, whereas MV has a 58.92% efficiency, MO has 35.44%, and MB has 29.24%. The photodecomposition of dyes is catalyzed mostly by •O2- and •OH-, as shown by research involving the trapping of radicals.

Tetracopper σ-Bound µ-Acetylide and -Diyne Units Stabilized by a Naphthyridine-based Dinucleating Ligand.

Reactions of a dicopper(I) tert-butoxide complex with alkynes possessing boryl or silyl capping groups resulted in formation of unprecedented tetracopper(I) µ-acetylide/diyne complexes that were characterized by NMR and UV-Vis spectroscopy, mass spectrometry and single-crystal X-ray diffraction. These compounds possess an unusual µ4-η1:η1:η1:η1 coordination mode for the bridging organic fragment, enforced by the rigid and dinucleating nature of the ligand utilized. Thus, the central π system remains unperturbed and accessible for subsequent reactivity and modification. This has been corroborated by addition of a fifth copper atom, giving rise to a pentacopper acetylide complex. This work may provide a new approach by which metal-metal cooperativity can be exploited in the transformation of acetylide and diyne groups to a variety of substrates, or as a starting point for the controlled synthesis of copper(I) alkyne-containing clusters.

Tetracopper σ‐Bound μ‐Acetylide and ‐Diyne Units Stabilized by a Naphthyridine‐based Dinucleating Ligand

AbstractReactions of a dicopper(I) tert‐butoxide complex with alkynes possessing boryl or silyl capping groups resulted in formation of unprecedented tetracopper(I) μ‐acetylide/diyne complexes that were characterized by NMR and UV/Vis spectroscopy, mass spectrometry and single‐crystal X‐ray diffraction. These compounds possess an unusual μ4‐η1:η1:η1:η1 coordination mode for the bridging organic fragment, enforced by the rigid and dinucleating nature of the ligand utilized. Thus, the central π system remains unperturbed and accessible for subsequent reactivity and modification. This has been corroborated by addition of a fifth copper atom, giving rise to a pentacopper acetylide complex. This work may provide a new approach by which metal‐metal cooperativity can be exploited in the transformation of acetylide and diyne groups to a variety of substrates, or as a starting point for the controlled synthesis of copper(I) alkyne‐containing clusters.

2p-4f Loop-chains {[Ln(hfac)3]2-radical}n achieved through multidentate nitronyl nitroxide radicals

Reactions of the designed multidenate nitronyl nitroxide radical ligands Nit-pH-3,5-bPy or Nit-pH-3,5-btrz (Nit-pH-3,5-bPy = 2-[3,5-bis(4-pyridyl)-phenyl]-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide; Nit-pH-3,5-btrz = 2-[3,5-bis(1H-1,2,4-triazol-1-yl)-phenyl]-4,4,5,5- tetramethylimidazoline-1-oxyl-3-oxide) with Ln(hfac)3 obtained four rare Ln-radical loop-chains, namely, {[Ln(hfac)3]2(Nit-pH-3,5-bPy)}n (LnIII = Gd 1, Tb 2; hfac = hexafluoroacetylacetonate) and {[Ln(hfac)3]2(Nit-pH-3,5-btrz)}n (LnIII = Tb 3, Ho 4). In all complexes, each pyridyl- or triazolyl-functionalized radical ligand is binded to four Ln(hfac)3 centers with a μ4-η1:η1:η1:η1-coordination mode through its two NO units and two N atoms of pyridines/triazoles, giving rise to interesting radical-bridged loop-chains with the scarcely reported 4f-2p-4f structural motifs. Magnetic measurements indicate that there are ferromagnetic interactions between the Ln(III) ions and the coordinated NO groups in these compounds. Tb 2 exhibits clear frequency-dependent out-of-phase (χ′′) signals in a zero dc field indicating slow relaxation of magnetization, while no non-zero χ′′ signals are observed for Tb 3 without an external magnetic field, which could be ascribed to the slightly different heterocyclic ligands.

Windmill-like ZnII-LnIII heterometallic compounds emited from visible to near infrared region

Considering the fascinating structural feature and special electronic property of heterometallic compounds, it is highly desirable but challenging to develop heterometallic species with excellent optical outputs. To this end, five ZnII-LnIII heterometallic compounds with the chemical composition of [Zn2Ln2(HL)2L2(NO3)4]∙xCH3OH∙yCH3CN∙zH2O (Zn2Ln2, LnIII = PrIII, NdIII, GdIII, TbIII and ErIII) based on ligand H2L, where 3-methoxysalicylamide and phenyl-substituted pyrazoloneimide are spaced by propylidene, have been developed. Single crystal analysis demonstrate that the new family of heterometallic compounds are all windmill-like ZnII-LnIII heterometallic species, where two fully deprotoned ligands L2− with μ3-η1:η1:η1:η2:η1 coordination mode in enol form and two partly deprotoned ligands HL− with μ2-η1:η1:η2 coordination mode in keto form are anchored by two ZnII and two LnIII ions. The luminescence studies indicate that the ZnII-L2−-HL− chromophore acts as a good antenna for sensitizing the visible emission of TbIII and near infraed emission of PrIII, NdIII and ErIII ions effectively as the result of its well matched triplet state. Experimental and computational studies on the energy level of the ZnII-incorporated antenna are performed for validating the energy transfer efficiency in these ZnII-LnIII heterometallic compounds. The results presented herein has important significance for the development of structural novel and luminescent ZnII-LnIII heterometallic compounds with wide emission ranges.

Reactions of Heterometallic Phosphinidene-Bridged MoMn and MoRe Complexes with Sulfur and Selenium: From Chalcogenophosphinidene- to Trithiophosphonate-Bridged Derivatives.

Reactions of [MoReCp(μ-PR*)(CO)6] with S8 were strongly dependent on experimental conditions (R* = 2,4,6-C6H2tBu3). When using 1 equiv of sulfur, complex [MoReCp(μ-η2:κ1S-SPR*)(CO)6] was slowly formed at 313 K, with a thiophosphinidene ligand unexpectedly bridging the dimetal center in the novel μ-κ1S:η2 coordination mode, as opposed to the μ-κ1P:η2 mode usually found in related complexes. The latter underwent fast decarbonylation at 363 K to give [MoReCp(μ-η2:η2-SPR*)(CO)5], with a six-electron donor thiophosphinidene ligand rearranged into the rare μ-η2:η2 coordination mode. Depending on reaction conditions, reactions with excess sulfur involved the addition of two or three S atoms to the phosphinidene ligand to give new complexes identified as the dithiophosphinidene-bridged complex [MoReCp(μ-η2:κ2S,S'-S2PR*)(CO)5], its dithiophosphonite-bridged isomer [MoReCp(μ-κ2S,S':κ2S,S'-S2PR*)(CO)5], or the trithiophosphonate-bridged derivative [MoReCp(μ-κ2S,S':κ2S,S'-S3PR*)(CO)5], all of them displaying novel coordination modes of their PRS2 and PRS3 ligands, as determined by X-ray diffraction studies. In contrast, the related MoMn complex yielded [MoMnCp(μ-η2:η2-SPR*)(CO)5] under most conditions. A similar output was obtained in reactions with gray selenium for either MoRe or MoMn phosphinidene complexes, which under different conditions only gave the pentacarbonyl complexes [MoMCp(μ-η2:η2-SePR*)(CO)5] (M = Re, Mn), these providing a new coordination mode for selenophosphinidene ligands.

Fabrication and DFT Calculation of Amine-Functionalized Metal-Organic Framework as a Turn-On Fluorescence Sensor for Fe3+ and Al3+ Ions.

Due to their important role in biological systems, it is urgent to develop a material that can rapidly and sensitively detect the concentration of Fe3+ and Al3+ ions. In this work, a brand-new CdII-based metal-organic framework [Cd(BTBD)2(AIC)]n (JXUST-18, BTBD = 4,7-bis(1H-1,2,4-triazol-1-yl)-2,1,3-benzothiadiazole and H2AIC = 5-aminoisophthalic acid) with a 4-connected sql topology was designed and synthesized. The symmetrical CdII centers are linked by AIC2- ligands with μ3-η1:η1:η1:η1 coordination mode to form a [Cd2(COO)2] secondary building unit (SBU). The contiguous SBUs are further connected by BTBD ligands to form a two-dimensional (2D) layer structure. JXUST-18 can remain stable in aqueous solutions with pH values of 3-12 or in boiling water. Luminescent experiments suggest that JXUST-18 displays more than eightfold fluorescence enhancement in the presence of Fe3+ and Al3+ ions, and the detection limits for Fe3+ and Al3+ ions are 0.196 and 0.184 μM, respectively. Furthermore, the change in luminescence color is uncomplicatedly distinguishable with the naked eye under ultraviolet light at 365 nm. In addition, a series of devices based on JXUST-18 including fluorescence test strips, lamp beads, and composite films were developed to detect metal ions via visual changes in luminescence color. Significantly, JXUST-18 is a rare MOF-based turn-on fluorescence sensor for the detection of Fe3+ ions. The theoretical calculation suggests that the complexation of Fe3+/Al3+ ions and the -NH2 group contributes to fluorescence enhancement.

Bonding Situation of σ-E-H Complexes in Transition Metal and Main Group Compounds.

The ambiguous bonding situation of σ-E-H (E=Si, B) complexes in transition metal compounds has been rationalized by means of Density Functional Theory calculations. To this end, the combination of the Energy Decomposition Analysis (EDA) method and its Natural Orbital for Chemical Valance (NOCV) extension has been applied to representative complexes described in the literature where the possible η1 versus η2 coordination mode is not unambiguously defined. Our quantitative analyses, which complement previous data based on the application of the Quantum Theory of Atoms in Molecules (QTAIM) approach, indicate that there exists a continuum between genuine η1 and η2 modes depending mainly on the strength of the backdonation. Finally, we also applied this EDA-NOCV approach to related main-group species where the backdonation is minimal.

Dinitrogen Binding at a Trititanium Chloride Complex and Its Conversion to Ammonia under Ambient Conditions

AbstractReaction of [TiCp*Cl3] (Cp*=η5‐C5Me5) with one equivalent of magnesium in tetrahydrofuran at room temperature affords the paramagnetic trinuclear complex [{TiCp*(μ‐Cl)}3(μ3‐Cl)], which reacts with dinitrogen under ambient conditions to give the diamagnetic derivative [{TiCp*(μ‐Cl)}3(μ3‐η1 : η2 : η2‐N2)] and the titanium(III) dimer [{TiCp*Cl(μ‐Cl)}2]. The structure of the trinuclear mixed‐valence complexes has been studied by experimental and theoretical methods and the latter compound represents the first well‐defined example of the μ3‐η1 : η2 : η2 coordination mode of the dinitrogen molecule. The reaction of [{TiCp*(μ‐Cl)}3(μ3‐η1 : η2 : η2‐N2)] with excess HCl in tetrahydrofuran results in clean NH4Cl formation with regeneration of the starting material [TiCp*Cl3]. Therefore, a cyclic ammonia synthesis under ambient conditions can be envisioned by alternating N2/HCl atmospheres in a [TiCp*Cl3]/Mg(excess) reaction mixture in tetrahydrofuran.

Dinitrogen Binding at a Trititanium Chloride Complex and Its Conversion to Ammonia under Ambient Conditions.

Reaction of [TiCp*Cl3] (Cp*=η5‐C5Me5) with one equivalent of magnesium in tetrahydrofuran at room temperature affords the paramagnetic trinuclear complex [{TiCp*(μ‐Cl)}3(μ3‐Cl)], which reacts with dinitrogen under ambient conditions to give the diamagnetic derivative [{TiCp*(μ‐Cl)}3(μ3‐η1 : η2 : η2‐N2)] and the titanium(III) dimer [{TiCp*Cl(μ‐Cl)}2]. The structure of the trinuclear mixed‐valence complexes has been studied by experimental and theoretical methods and the latter compound represents the first well‐defined example of the μ3‐η1 : η2 : η2 coordination mode of the dinitrogen molecule. The reaction of [{TiCp*(μ‐Cl)}3(μ3‐η1 : η2 : η2‐N2)] with excess HCl in tetrahydrofuran results in clean NH4Cl formation with regeneration of the starting material [TiCp*Cl3]. Therefore, a cyclic ammonia synthesis under ambient conditions can be envisioned by alternating N2/HCl atmospheres in a [TiCp*Cl3]/Mg(excess) reaction mixture in tetrahydrofuran.

Revealing the Role of the Cyaphide Ion as a Bridging Ligand in Heterometallic Complexes.

The synthesis of heterometallic transition metal complexes featuring bridging cyaphide ions (C≡P−) is reported. These are synthesized from reactions of Au(IDipp)(CP) (IDipp=1,3‐bis(2,6‐diisopropylphenyl)imidazol‐2‐ylidene) with electron‐rich, nucleophilic transition metal reagents, affording Au(IDipp)(μ2−C≡P)Ni(MeI i Pr)2 (MeI i Pr=1,3‐diisopropyl‐4,5‐dimethylimidazol‐2‐ylidene) and Au(IDipp)(μ2−C≡P)Rh(Cp*)(PMe3). These studies reveal that, in contrast to the cyanide ion, bimetallic cyaphido complexes strongly favor a η1 : η2 coordination mode that maximizes the interaction of the second metal (Ni, Rh) with the π‐manifold of the ion (and not the phosphorus atom lone pair). End‐on bridging can be effectively unlocked by blocking the π‐manifold, as demonstrated by reaction of Au(IDipp)(μ2−C≡P)Rh(Cp*)(PMe3) with an electrophilic transition metal reagent, W(CO)5(THF), which affords the heterotrimetallic compound Au(IDipp)(μ3−C≡P)[Rh(Cp*)(PMe3)][W(CO)5].

Revealing the Role of the Cyaphide Ion as a Bridging Ligand in Heterometallic Complexes

AbstractThe synthesis of heterometallic transition metal complexes featuring bridging cyaphide ions (C≡P−) is reported. These are synthesized from reactions of Au(IDipp)(CP) (IDipp=1,3‐bis(2,6‐diisopropylphenyl)imidazol‐2‐ylidene) with electron‐rich, nucleophilic transition metal reagents, affording Au(IDipp)(μ2−C≡P)Ni(MeIiPr)2 (MeIiPr=1,3‐diisopropyl‐4,5‐dimethylimidazol‐2‐ylidene) and Au(IDipp)(μ2−C≡P)Rh(Cp*)(PMe3). These studies reveal that, in contrast to the cyanide ion, bimetallic cyaphido complexes strongly favor a η1 : η2 coordination mode that maximizes the interaction of the second metal (Ni, Rh) with the π‐manifold of the ion (and not the phosphorus atom lone pair). End‐on bridging can be effectively unlocked by blocking the π‐manifold, as demonstrated by reaction of Au(IDipp)(μ2−C≡P)Rh(Cp*)(PMe3) with an electrophilic transition metal reagent, W(CO)5(THF), which affords the heterotrimetallic compound Au(IDipp)(μ3−C≡P)[Rh(Cp*)(PMe3)][W(CO)5].

Tuning Photophysical Properties by p-Functional Groups in Zn(II) and Cd(II) Complexes with Piperonylic Acid

Aggregation between discrete molecules is an essential factor to prevent aggregation-caused quenching (ACQ). Indeed, functional groups capable of generating strong hydrogen bonds are likely to assemble and cause ACQ and photoinduced electron transfer processes. Thus, it is possible to compare absorption and emission properties by incorporating two ligands with a different bias toward intra- and intermolecular interactions that can induce a specific structural arrangement. In parallel, the π electron-donor or electron-withdrawing character of the functional groups could modify the Highest Ocuppied Molecular Orbital (HOMO)–Lowest Unocuppied Molecular Orbital (LUMO) energy gap. Reactions of M(OAc)2·2H2O (M = Zn(II) and Cd(II); OAc = acetate) with 1,3-benzodioxole-5-carboxylic acid (Piperonylic acid, HPip) and 4-acetylpyridine (4-Acpy) or isonicotinamide (Isn) resulted in the formation of four complexes. The elucidation of their crystal structure showed the formation of one paddle-wheel [Zn(μ-Pip)2(4-Acpy)]2 (1); a mixture of one dimer and two monomers [Zn(µ-Pip)(Pip)(Isn)2]2·2[Zn(Pip)2(HPip)(Isn)]·2MeOH (2); and two dimers [Cd(μ-Pip)(Pip)(4-Acpy)2]2 (3) and [Cd(μ-Pip)(Pip)(Isn)2]2·MeOH (4). They exhibit bridged (1, µ2-η1:η1), bridged, chelated and monodentated (2, µ2-η1:η1, µ1-η1:η1 and µ1-η1), or simultaneously bridged and chelated (3 and 4, µ2-η2:η1) coordination modes. Zn(II) centers accommodate coordination numbers 5 and 6, whereas Cd(II) presents coordination number 7. We have related their photophysical properties and fluorescence quantum yields with their geometric variations and interactions supported by TD-DFT calculations.

Heteroleptic Rare-Earth Tris(metallocenes) Containing a Dibenzocyclooctatetraene Dianion.

Isolable heteroleptic tris(metallocenes) containing five-membered and larger rings remain extremely scarce. The utilization of tripositive rare-earth-metal ions with ionic radii >1 Å allowed access to unprecedented and sterically congested dibenzocyclooctatetraenyl (dbCOT) metallocenes, [K(crypt-222)][Cptet2RE(η2-dbCOT)] (RE = Y (1), Dy (2); Cptet = tetramethylcyclopentadienyl), through a salt metathesis reaction involving Cptet2RE(BPh4) and the potassium salt of the dbCOT dianion. The solid-state structures were investigated by single-crystal X-ray diffraction, magnetometry, and IR spectroscopy and provided evidence for the first crystallographically characterized (dbCOT)2- anion in a complex containing d- or f-block metals. Remarkably, the (Cptet)- ligands force a distortion from planarity within the (dbCOT)2- moiety, engendering a rare η2-bonding motif, as opposed to the classical η8 conformation observed in complexes bearing a (COT)2- ion. The η2 coordination mode was proven crystallographically between 100 and 298 K and computationally (DFT and NBO). Furthermore, nucleus independent chemical shift (NICS) calculations uncovered significant ring current within the dbCOT ligand. The solution-state properties of 1 and 2 were analyzed via cyclic voltammetry, NMR, and UV-vis spectroscopy. Cyclic voltammograms of 1 and 2 exhibit a quasi-reversible feature indicating the accessibility of complexes with dbCOT in two oxidation states (dbCOT2-/3-•). Importantly, the dysprosium congener, 2, is a zero-field single-molecule magnet (SMM).

Bis(η5-cyclo-penta-dien-yl)(2-{[(2-meth-oxy-phen-yl)imino]-meth-yl}phenolato-κ3 O,N,O')terbium.

The air- and moisture-sensitive title compound, [Tb(C5H5)2(C14H12NO2)], was synthesized from tris-(cyclo-penta-dien-yl)(tetra-hydro-furan)-terbium and 2-{[(2-meth-oxy-phen-yl)imino]-meth-yl}phenol. Each Tb atom is coordinated by two cyclo-penta-dienyl ligands in an η5-coordination mode and by one N and two O atoms of the organic ligand in a tridentate κ3 O,N,O'-mode.

A highly sensitive and multi-responsive Tb-MOF fluorescent sensor for the detection of Pb2+, Cr2O72−, B4O72−, aniline, nitrobenzene and cefixime

A terbium metal organic framework (Tb-MOF), namely {[Tb(dppa)(H2O)2]·dima·H2O·0.5O}n (1), (H4dppa = 5-(3′4′-dicarboxylphenoxy)isophthalic acid, dima = dimethylamine, which is formed by the decomposition of DMF in aqueous solution at high temperature.) was prepared and characterized. Tb-MOF is connected by (dppa)4- ligands via μ4:η1,η2,η2,η2 coordination mode to form a two-dimensional wavy network, which is extended to three-dimensional supramolecular structures based on hydrogen bonding. Tb-MOF has excellent fluorescence properties, which can be used for fluorescence recognition and quantitative determination of cation and anion, antibiotics and small organic molecules in aqueous solution with high sensitivity and good selectivity. Tb-MOF showed enhanced fluorescene for Pb2+ and B4O72− ions, while quenching fluorescence for Cr2O72− ion. Noticeably, this is the first time that Pb2+ and B4O72− ions have been detected by a MOF-based fluorescence sensor using a fluorescence enhancement mechanism. More interestingly, Tb-MOF can quantitatively detect aniline (ANI) in aqueous solution by ratiometric fluorescence sensing. In addition, Tb-MOF has great selectivity and sensitivity for detecting of nitrobenzene (NB) and cefixime (CEF). In particular, when NB concentration is 50 μM, the fluorescence quenching rate of Tb-MOF reaches 99.6%. Therefore, this paper introduces a highly sensitive and multi-responsive Tb-MOF sensor, which can be used to detect Pb2+, B4O72−, Cr2O72−, ANI, NB and CEF with fast response speed and good selectivity.